Adhesive paper material and a label made from such material

ABSTRACT

A web for the production of self-adhesive paper labels consists of thin paper web and a very thin plastic sheet of polyester or a similar material of high tensile strength and low initial stretchability, yet of low tear strength due to its small thickness, e.g. 12 μm. Labels of such a web show a high tensile strength and a good flexibility, while they show a sufficient low tear strength to be usable as guarantee labels. In the production of the labels as left on a co-laminated backing sheet the so-called `waste` may be drawn off at high speed, whereby the production may run at increased speed.

The present invention relates to an adhesive paper sheet or web materialand to labels made from such material.

Conventional self-adhesive paper labels consist of a rather strong,printable paper, usually of the specific weight 80 g/m². The rear sideof the paper is provided with a pressure sensitive adhesive as coveredby a backing or carrier sheet, which is treated or impregnated with anormally silicone based slip agent so as to be easily removable from theadhering side of the paper label just prior to use thereof. The backingsheet, in addition to its mere cover purpose, also serves to protect theadhesive from drying out, and a further important purpose thereof isconnected with the production of the labels: Normally the single labelsare produced on a continuous web of the backing sheet material asoriginally carrying a corresponding continuous paper web, the labelsbeing provided as mutually spaced paper areas remaining on the backingweb upon the paper web being cut to define these areas and upon thepaper web outside these areas being removed from the backing web. Theseoperations may take place in a continuous manner, e.g. in connectionwith the web passing a printing machine, whereby the label areas areprinted and cut free of the surrounding paper, without the backing webbeing correspondingly cut. The said surrounding paper occurs as acontinuous paper web having one or more rows of holes corresponding tothe labels, and this web, the so-called "waste", is continuously drawnoff the backing web so as to leave the backing web with one or more rowsof mutually spaced paper labels. This product may be rolled up or cutinto sheet members as carrying one or more labels, whether printed ornot.

The said drawing off of the "waste" web from the backing web is abottleneck operation as far as the production speed is concerned,because for a high speed of production it is necessary to exert a strongpull in the waste web, i.e. this perforated web should correspondinglyshow a high tensile strength. The said specific paper weight of 80 g/m²as generally used for the label paper refers to a paper, which is inmost cases unnecessarily thick for the very labelling purpose, butnecessary for enabling the production to run reasonably quickly withoutbeing stopped by ruptures of the drawn off waste web.

The use of a rather heavy paper quality for the label web may thus beseen as a compromise, and it is a more or less lucky compromise evenfrom other and more special points of view. Thus, a special andimportant field of application of self-adhesive labels is a so-calledguarantee sealing of packings or boxes, whereby a label as placed acrossa separation line between two material portions such as the body and thelid of a container should be able to generally resist considerableforces acting in the plane of the label material, while on the otherhand the label should not be strong enough to enable unauthorizeddrawing off and remounting thereof, i.e. the label should be liable tobe broken in a visible manner when attempts are made to draw it off thesurface, on which it is mounted. In other words, the tearing offstrength of the label should be smaller than the strength with which itadheres to the mounting surface, i.e. the tear strength should be rathersmall, while the general tensile strength should still be rather highfor enabling a reasonably high production speed as mentioned above.These considerations, of course, are bound to lead to some compromise asto the strength of the paper, and generally the known compromises havebeen far from being really satisfactory.

In the said special field of application of the labels there are evenfurther problems as connected with the flexibility of the label paper.When a label is applied across a separation line between mutuallyslightly movable elements such as the body and the lid of a container,the label should resist not only separation forces between theseelements, but even compression forces between the elements, whereby thelabel will be liable to bulge out in the local area just outside thesaid separation line. Such local and narrow bulging of the label maywell result in a label fracture even if the general tensile strength ofthe material is high, and such fractures are experienced quite ofteneven when the paper material is as strong as corresponding to the saidspecific weight of 80 g/m². A label fracture along the separation linebetween the box and the lid portion of a container may cause serioustroubles, if the label constitutes an authorized sealing means, e.g. ona meat container by transit shipping thereof. It has been suggested toreinforce the labels against fracturing by applying ordinary tape to thepaper along the edge areas thereof, but this tends to make the labelsunsuitably stiff, and besides such a reinforcing also tends to make iteasier to effect unauthorized removal and remounting of the label,because the label is then easier to draw off its mounting surfacewithout being ruptured thereby.

It is the purpose of the invention to provide an improved label sheetmaterial, which is particularly advantageous for both the production andthe use of the labels.

According to the invention the label sheet material comprises a verythin plastic sheet of high specific stiffness, which is arranged betweenthe rear side of the paper sheet and the layer of adhesive, i.e. theplastic sheet is bonded at one side to the paper sheet and carries thelayer of adhesive at its opposite side. Generally, the tensile strengthand tearing strength of sheet materials of plastics are higher than forordinary paper, but several plastic sheet materials, when beingrelatively stiff and very thin, have proved to show a general tensilestrength, which, compared with paper, is still relatively high, whilethe tearing strength is not very high. Thus, a practically non-resilientpolyester sheet with a thickness of only some 0.01 mm will add to thegeneral tensile strength of the associated paper sheet, while it willnot add correspondingly to the tearing strength thereof.

Therefore, a paper label as reinforced by a very thin plastic sheet oflow stretchability on its rear side will still be usable as a guaranteelabel, because its tear strength is still sufficiently low to make thelabel rupture when it is sought to be drawn off its mounting surface,provided, of course, that the adhesive is of a good quality. Obviously,a material of high specific rigidity will be stiff even against bending,but with a thickness of only some 10-20 μm the plastic sheet materialwill be perfectly flexible anyway.

The reinforcement with respect to the tensile strength is important forthe general strength of the labels, but in fact there are two mainaspects which should here be separately considered:

One of these main aspects relates to the production of the labels. Theuse of a generally reinforced web material as here discussed has shown aremarkable advantage in the production of the labels, viz. that the said"waste" can be safely pulled off at a considerably increased speed,whereby the general production speed in the label printing and formingprocess can be correspondingly increased.

The other of said two main aspects is that a satisfactory tensilestrength of the labels is now obtainable with the use of a paper ofreduced thickness, viz. with a preferred specific weight of about 60g/m². The resulting tensile strength is satisfactory not only for thelabels, in use, but even for the production, because the "waste" maystill be pulled off at high speed.

The primary purpose of the label paper is to receive a desired printingand even hand writing, and this purpose is of course fulfilled even whenthe paper is relatively thin and therewith also cheap. Such a thinpaper, however, also contributes to an increased flexibility of thelabel, and the additional use of an extremely thin plastic sheet, asmentioned, does not substantially counteract such an increasedflexibility while it adds to the flexing suppleness. Therefore, with theuse of the paper of reduced thickness as practically conditioned by theinvention, the labels will be flexible enough to be non-sensible tolocal bulgings, and also for this reason, therefore, the labels will beextremely well suited for use as guarantee labels to be mounted acrossthe separation line between a container and a lid or another coverthereof. Also, the thin and flexible labels are mountable on surfaces ofnon-planar shape better than conventional, less flexible labels.

Plastic sheet materials as here referred to for use as a reinforcingmaterial inherently show the characteristic of being very tight,irrespective of the desired small thickness of the sheet. This leads toa further advantage, viz. that the plastic sheet, when unperforated,forms a sealing membrane between the paper and the adhesive, whereby thelatter is prevented from intruding into the paper. So far it has beenfound natural that the adhesive tends to intrude into the paper, andproblems have even existed in preventing the adhesive from later onoccuring on the front side of the paper. It has been quite customary tooverdose the adhesive to the paper just for making sure that theadhesive would remain surface active. Attempts have been made to providefor a barrier layer between the adhesive and the paper, but so far notwith commercial success and not based on the use of a sheet materialadding tensile strength to the product.

Thus, the preferred use of a thin label paper in combination with thesaid very thin plastic sheet does not involve any increased risk of theadhesive "bleeding" through the paper. The plastic sheet is, easilybonded to the paper e.g. by means of a lacquer, and with the use of theplastic sheet the adhesive itself may be applied according to minimumrequirements, without the said usual overdosage.

The problem as to the adhesive bleeding through the paper has beenpronounced particularly with labels to be mounted on non-poroussurfaces, and for some special labels the paper has been substituted bya more expensive plastic sheet material, which, however, involves anexpensive printing technique and a subsequent covering lamination orlacquering. Standard labels according to the invention will be perfectlyusable for a long row of both general and special applications, and theyare, if desired, very easy to provide with a lacquer layer subsequent tothe simple printing thereof. Hereby the labels will be particularlymoisture resistant, as desirable e.g. when they are used with a tear-offcopy on various spare parts, for facilitating reordering thereof.

Preferably, the thin plastic sheet is applied to the paper as acontinuous web all over the rear paper side, but it will be within thescope of the invention to arrange the plastic web stripwise only, e.g.as two or more parallel, mutually spaced strips extending in thedirection of the label as relevant for the orientation of a desiredincreased tensile strength thereof. The label may of course still beprovided with adhesive over its entire rear side, and if the plasticstrips are bonded to the paper by means of a lacquer as evenly appliedto the paper, then the lacquer surface as exposed between the strips mayof course receive the adhesive and even constitute, itself, a barrieragainst the adhesive entering into the paper.

It should be mentioned that the use of the said relatively thin paper inthe label material, as advantageous for rendering the labels more suppleand flexible with several important consequences, also accounts for theadvantage that piles or rolls of a label carrying sheet material willhold a relatively high number of labels for any given size of the pileor roll.

At this place it should be emphasized once again that another specificadvantage of the invention is the possibility of processing the combinedlabel and backing web in an ordinary label printing and cutting machinewith a remarkably high speed, because the "waste" can be pulled off byan applied high pulling force at high speed without the perforated wasteweb being ruptured.

In the following some examples of the production of a label material webaccording to the invention are given:

EXAMPLE 1

One side of a paper web of a non-glossy, printable paper having athickness corresponding to 60 g/m² is successively provided with a thinlacquer layer and is then successively laid together with a sheetmaterial web of polyester (PETP-film 12 μm, Eura Paper, Finland) havinga thickness of 0.012 mm (12 μm). This combined web is laminated togetherwith a silicone impregnated carrier paper, which, prior to itsengagement with the said combined web, has received a thin surface layerof a pressure sensitive adhesive of a conventional type, whereby theadhesive is brought to stick to the polyester sheet.

EXAMPLE 2

A paper web of a printable paper having a thickness corresponding to40-60 g/m² and already at one side being coated with a thin plasticsheet of low resiliency or stretchability, e.g. polyester, as laminatedto the paper by means of a hot melt glue, is provided with a thin layerof a pressure sensitive adhesive on its sheet covered side, whereafterthis adhering side is covered by a substantially non-adhering,impregnated paper web.

EXAMPLE 3

To one side of a non-glossy, printable paper web (70 g/m²) is applied anunbroken lacquer layer, whereafter the same paper web side is laidtogether with a number of mutually spaced, parallel, thin plastic sheetstrips (8-20 μm) of low stretchability. The paper web as thus reinforcedis laid together with a silicone treated carrier web as provided with alayer of a pressure sensitive adhesive.

While in the foregoing reference has been made to self-adhesive labelscomprising a pressure sensitive adhesive, it will be appreciated thatthe nature of the adhesive is not decisive for the majority of featuresand advantages of the invention, and it should be mentioned, therefore,that the invention is not limited to any specific type of adhesive Thus,a conventional moisture actuated glue or a heat actuated adhesive wouldbe applicable.

When a low tear off resistance of the labels is desired it will beadvantageous to additionally use a known measure for reducing thisresistance, viz. to provide the labels and now the associated plasticsheet with PG,11 a series of edge notches, whereby a label rupture ismore easily initiated.

The invention also comprises the disclosed methods of manufacturing alabel web, whereby an important advantage is that the said waste may bedrawn off at high speed.

We claim:
 1. A web of a label sheet material comprising a printablepaper laying having a layer of an adhesive at one side thereof,characterized in that the material further comprises a very thin plasticsheet interposed between the paper and the adhesive, the plastic sheetbeing bonded to the paper and being of a material which has a hightensile strength and a low initial extensibility, the very thin plasticsheet having a sufficiently higher tensile strength and sufficiently lowinitial extensibility such that the printable paper layer is reinforcedand a label can be provided from said label sheet material whose tearstength is low so that the label cannot be removed from its mountingsurface without rupture of the label.
 2. A web according to claim 1, inwhich the plastic sheet has a thickness of 5-40 μm.
 3. A web accordingto claim 2, wherein the plastic sheet has thickness of 10-15 μm.
 4. Aweb according to claim 1, in which the plastic sheet is provided asparallel, mutually spaced strips on the paper.
 5. A web according toclaim 4, in which the strips are bonded to the paper by a layer oflacquer, which layer of lacquer is present on the paper also between thestrips.
 6. A label as produced from a web according to any one of claims1,2,4 or
 5. 7. A web according to claim 1, in which the thickness of thepaper material corresponds to about 40-70 g/m².
 8. A web according toclaim 1, in which said plastic shedt is made of a polyester material. 9.A web according to claim 1, further including a backing web adjacent thelayer of adhesive at a side of said layer of adhesive opposite to theside thereof nearest the printable paper layer.
 10. A web according toclaim 1, wherein said plastic sheet is made of a material that preventsthe adhesive, of the layer of adhesive, from intruding into theprintable paper layer.
 11. A web according to claim 1, wherein theplastic sheet is provided as a continuous web on the paper.
 12. A webaccording to claim 1, wherein said label sheet material constitutes amaterial to provide guarantee sealing of articles having at least twoportions movable relative to each other, whereby a label formed of saidlabel sheet material, placed across a separation line between two ofsaid at least two portions, can resist forces acting in the plane of thelabel while not being strong enough to enable drawing off and remountingof the label across said separation line.
 13. A label as produced from aweb according to claim 12.